Transfer case with integrated planetary gear assembly and &#34;on-demand&#34; four-wheel drive

ABSTRACT

Provided is a transfer case having an integrated planetary gear assembly is operably installed between an input member and first and second output members and constructed in a compact dual-planetary arrangement having dual sun gears and dual planet gears that are journally supported from a carrier. The planetary gear assembly is axially slidable relative to the input and output members to a number of positions for establishing various drive modes. Included among the drive modes is a two-wheel with on-demand four-wheel drive high-range mode. In this arrangement, the carrier is driven by the input member, and the first output is engaged with the carrier for providing two-wheel drive output. The carrier is further coupled to the input member of a torque coupling device. The torque coupling device is operable to sense relative rotation between the first and second output members and to deliver torque to the second output member in response to a loss of traction at the first output member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 08/148,470, filedNov. 5, 1993, now allowed, and entitled "Full-Time Integrated PlanetaryFour-Wheel Drive Transfer Case With Traction", which is acontinuation-in-part of Ser. No. 07/961,486, filed Oct. 15, 1992, nowU.S. Pat. No. 5,284,068, and entitled "Transfer Case With IntegratedPlanetary Gear Assembly".

BACKGROUND OF THE INVENTION

The present invention relates generally to transfer cases for four-wheeldrive vehicles and, more particularly, to such a transfer case having agear reduction unit and an inter-axle differential "integrated" into aplanetary gear assembly for providing a variety of part-time andfull-time four-wheel drive operating modes.

Modernly, many light-duty and sport-utility vehicles are equipped with apower transfer unit, such as a four-wheel drive transfer case, forproviding a four-wheel drive mode of operation. To accommodate differingroad surfaces and conditions, many four-wheel drive transfer cases areequipped with a gear reduction unit for providing a high-range (i.e.,direct drive) and a low-range (i.e., reduced ratio drive) in conjunctionwith the four-wheel drive mode. Most commonly, the gear reduction unitsused in four-wheel drive transfer cases include either a layshaftarrangement or a planetary gear assembly. In addition, some transfercases are also equipped with an interaxle differential mechanism forpermitting torque proportioning and differential speed variationsbetween the front and rear axles of the four-wheel drive vehicle.Reference may be made to U.S. Pat. No. 4,677,873 for disclosure of anexemplary four-wheel drive transfer case equipped with a planetary gearreduction unit and a planetary interaxle differential mechanism.

In an effort to minimize the overall size of transfer cases, it has beenproposed to incorporate the gear reduction unit and the interaxledifferential mechanism into a single planetary gear assembly. One sucharrangement is described in U.S. Pat. No. 4,644,822 which discloses atransfer case having "back-to-back" first and second planetary gear setshaving common components which can be selectively shifted as a unit toestablish the different four-wheel drive modes. In addition, U.S. Pat.Nos. 4,677,875, 4,344,335, 4,215,593 and 4,805,484 each disclose atransfer case having a single planetary gear assembly which is operableto establish various drive modes through manipulation of one or moresuitable shift mechanisms. While such prior art arrangements provide acompact construction, there is a continuing need to develop low cost,simplified alternatives which meet modern requirements for low noise andweight.

SUMMARY OF THE INVENTION

It is therefore an abject of the present invention to provide a transfercase for a four-wheel drive vehicle having an "integrated" planetarygear assembly which incorporates a gear reduction unit and an interaxledifferential mechanism into a single unit. The integrated planetary gearassembly is adapted to be selectively shifted between various operatingpositions for establishing a two-wheel drive mode, a part-timefour-wheel high-range mode, a full-time four-wheel high-range mode, anda part-time four-wheel low-range mode. As a related object, anadditional operating position is provided for defining a neutral mode toaccommodate towing of the vehicle.

Another object of the present invention is to provide a transfer casefor a four-wheel drive vehicle having an integrated planetary gearassembly which incorporates a gear reduction unit and an interaxledifferential mechanism into a single unit for providing a two-wheeldrive high-range mode, two-wheel drive high-range with "on-demand"four-wheel drive high-range mode, part-time four-wheel high-range modeand a part-time four-wheel low-range mode. The transfer case of thepresent invention includes a torque transfer device operably associatedwith the integrated planetary assembly for selectively transferring thetorque output of the integrated planetary assembly to the secondtransfer case output for initiating on-demand four-wheel drive mode.

According to a preferred embodiment of the present invention, theintegrated planetary gear assembly is operably installed between aninput member and first and second output members of the transfer caseand is constructed in a compact dual-planetary arrangement having dualsun gears and dual planet gears that are journally supported from acarrier. In the two-wheel drive mode, the carrier is rotatably driven bythe input member and is coupled to the first output member fortransferring drive torque thereto. In the part-time four-wheelhigh-range mode, the carrier directly couples the input member to bothof the first and second output members so as to inhibit differentialaction therebetween. In the full-time four-wheel high-range mode, thecarrier is driven by the input member while the first and second sungears respectively engage the first and second output members in amanner facilitating differential action and torque proportioningtherebetween. When shifted to the neutral mode, the first and second sungears are disengaged from their respective output members such that nodrive torque is transferred from the input member and carrier to eitherof the first and second output members. Finally, upon movement of theplanetary gear assembly to the part-time four-wheel low-range mode, thecarrier is directly coupled to both of the first and second outputmembers, the first sun gear is coupled to the input member and thesecond sun gear is coupled to a grounded member such that the carrier isrotatably driven at a reduced speed and no differentiation between theoutput members is permitted.

In another preferred embodiment of the present invention, the integratedplanetary gear assembly is operably installed between an input memberand first and second output members of the transfer case and isconstructed in a compact dual-planetary arrangement having dual sungears and dual planet gears that are journally supported from a carrier.In the two-wheel drive mode, the carrier is rotatably driven by theinput member and is coupled to the first output member for transferringdrive torque thereto. In the part-time four-wheel high-range mode, thecarrier directly couples the input member to both of the first andsecond output members so as to inhibit differential action therebetween.When shifted to the neutral mode, the carrier is disengaged from therespective input and output members such that no drive torque istransferred from the input member and carrier to either of the first andsecond output members. Upon movement of the planetary gear assembly tothe part-time four-wheel low-range mode, the carrier is directly coupledto both of the first and second output members, the first sun gear iscoupled to the input member and the second sun gear is coupled to agrounded member such that the carrier is rotatably driven at a reducedspeed and no differentiation between the output members is permitted. Inthe two-wheel with on-demand four-wheel high-range mode, the carrier isdriven by the input member. The first output is engaged with the firstsun gear for providing two-wheel drive output. The carrier is furthercoupled to the input of a torque transfer device. The torque transferdevice is operable to sense relative rotation between the first andsecond output members and to deliver torque to the second output memberin response to a loss of traction at the first output member.

Additional objects, features and advantages of the present inventionwill become apparent from studying the following detailed descriptionand appended claims when taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an exemplary four-wheel drive transfercase incorporating an integrated planetary gear assembly constructed inaccordance with a preferred embodiment of the present invention;

FIG. 2 is an enlarged fragmentary view of FIG. 1 illustrating theintegrated planetary gear assembly in a two-wheel high-range mode;

FIG. 3 is an enlarged fragmentary view of FIG. 1 showing the integratedplanetary gear assembly in a part-time four-wheel high-range mode;

FIG. 4 is a view, similar to FIG. 3, showing the integrated planetarygear assembly in a full-time four-wheel high-range mode;

FIG. 5 is a view, similar to FIG. 3, showing the integrated planetarygear assembly in a neutral mode;

FIG. 6 is a view similar to FIG. 3, showing the integrated planetarygear assembly in a part-time four-wheel low-range mode;

FIG. 7 is a partial sectional view illustrating an alternativeconstruction for an integrated planetary gear assembly that can bereadily incorporated into the transfer case shown in FIG. 1;

FIG. 8 is a partial sectional view illustrating another alternativeconstruction for an integrated planetary gear assembly that can bereadily incorporated into the transfer case shown in FIG. 1 and furtherillustrating the torque transfer device associated with the integratedplanetary gear assembly in accordance with a preferred embodiment of thepresent invention;

FIG. 9 is an enlarged fragmentary view of FIG. 8 showing the integratedplanetary gear assembly in a neutral mode;

FIG. 10 is a view similar to FIG. 9 showing the integrated planetarygear assembly in a two-wheel high-range mode;

FIG. 11 is a view similar to FIG. 9 showing the integrated planetarygear assembly in a part-time four-wheel low-range mode;

FIG. 12 is a view similar to FIG. 9 showing the integrated planetarygear assembly in a two-wheel with on-demand four-wheel high-range mode;and

FIG. 13 is a view similar to FIG. 9 showing the integrated planetarygear assembly in a part-time four-wheel high-range mode.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present invention relates to the arrangement of a gearreduction unit and an interaxle differential mechanism as an integratedplanetary-type gear assembly which is adapted for use in the transfercase of a four-wheel drive motor vehicle. The integrated planetary gearassembly of the present invention offers the advantages of a compactarid simplified structure, reduced weight, quiet operation andelimination of an internally toothed annulus gear which is commonly usedin conventional arrangements. The present invention further provides foroperably interconnecting a torque transfer device to the integratedplanetary gear assembly for, when the transfer case is in a two-wheeldrive mode, selectively coupling the torque output of the integratedplanetary assembly to the second output of the transfer case forproviding an on-demand four-wheel drive mode.

With particular reference to FIG. 1 of the drawings, there is shown anexemplary transfer case 10 according to a preferred embodiment of thepresent invention and of the type adapted for use in virtually any fourwheel drive motor vehicle. As is known, transfer case 10 is operable forselectively transferring power (i.e., drive torque) from the motorvehicle's drivetrain (i.e., engine and transmission) to its front andrear axle assemblies. According to the construction shown, transfer case10 includes a housing 12 that is adapted to receive a transmissionoutput shaft (not shown) from the vehicle's drivetrain for rotationabout a longitudinal axis 14. More specifically, an input shaft 16 isaligned for rotation along central axis 14 and has internal splines 18that engage the external splines of the transmission output shaft. Inputshaft 16 is supported for rotation in housing 12 by a bearing assembly20 and is retained therein by an annular collar 22 secured to housing 12such as by a plurality of screws 24. An externally toothed input gear 26is integrally formed on input shaft 16 for transferring drive torquefrom the transmission output shaft to a combination gear reduction unitand interaxle differential mechanism, hereinafter referred to asintegrated planetary gear assembly 28. As will be discussed hereinafter,integrated planetary gear assembly 28 is operably installed betweeninput shaft 16 and first and second output members for axial slidingmovement relative thereto. Such axial movement of integrated planetarygear assembly 28 is adapted to establish various driving relationshipsbetween the first output member and the second output member which arerespectively coupled to the motor vehicle's rear and front axleassemblies in a known manner.

With reference to FIGS. 1 and 2, the first output member of transfercase 10 is shown as a rear output shaft 30 which is alignedconcentrically about longitudinal axis 14 and has a piloted end portion34 that is journally supported via a suitable bearing assembly 36 withinan axial counter-bore 38 formed in input shaft 16. Rear output shaft 30has a radial extension 42 on which first and second sets of laterallyspaced external clutch teeth 44 and 46, respectively, are formed. Inaddition, an elongated quill sleeve 48 surrounds rear output shaft 30adjacent radial extension 42. Quill sleeve 48 is grounded (i.e., fixed)at a first end to housing 12 via a reaction flange 50 while externalsplines 52, formed at the second end of quill sleeve 48, engage internalspines 53 formed on an annular reaction ring 54. Thus, reaction ring 54is non-rotatably supported on quill sleeve 48. In addition, reactionring 54 is further shown to include external clutch, teeth 56 that arelongitudinally alignable with the first and second sets of clutch teeth44 and 46, respectively, on rear output shaft 30. A tubular drive sleeve58 is concentric with and supported on quill sleeve 48. Thus, reactionring 54 is interposed between radial extension 42 of rear output shaft30 and drive sleeve 58. In addition, drive sleeve 58 includes first andsecond sets of laterally spaced external clutch teeth 60 and 62,respectively. According to the first preferred embodiment of the presentinvention, a shift arrangement is provided for permitting the vehicleoperator to selectively shift transfer case 10 between the varioustwo-wheel and four-wheel drive modes. According to the embodiment shownin FIGS. 1 through 6, the shift arrangement would be operable forcoupling drive sleeve 58 to a drive sprocket 68 which, in turn, isinterconnected to the second output member of transfer case 10.Preferably, a synchronizer clutch apparatus 66 is provided to permit"on-the-fly" shifting of transfer case 10 between the two-wheelhigh-range drive mode and the four-wheel high-range drive mode.Synchronizer clutch apparatus 66 is operably located between drivesleeve 58 and drive sprocket 68 which is journally supported forrotation on quill sleeve 48 via suitable bearings assemblies 70. Whilesynchronizer apparatus 66 can be of any conventional construction, it ispreferably of the cone type disclosed in commonly owned U.S. Pat. No.5,105,927, the disclosure of which is expressly incorporated byreference herein. However, it should be understood that any suitablesynchronizer apparatus could be used without departing from the fairscope of the present invention.

With continued reference to FIG. 2, synchronizer clutch apparatus 66 isshown to include a hub 72 having an inner axial flange portion 74 fixedto drive sleeve 58 for rotation therewith. Hub 72 also includes aradially extending web portion 76 which has a longitudinally extendingcylindrical portion 78 formed at its periphery. External splines 80 areformed on cylindrical portion 78 which are adapted to slidingly receiveinternal splines 82 of a "mode" shift sleeve 84 thereon. Thus, modeshift sleeve 84 is rotatable with and axially moveable relative to hub72 in a well known manner by means of engagement of a suitable shiftmember (not shown) within an annular groove 86 formed in shift sleeve84. As is known, axial movement of mode shift sleeve 84 from its centralnon-actuated position (FIG. 2) toward drive sprocket 68 causesfrictional interaction between blocker ring 88, clutch cone 90 and innercone 92. Such frictional interaction results in speed synchronizationbetween mode shift sleeve 84 (and drive sleeve 58) and drive sprocket68, thus allowing internal splines 82 of mode shift sleeve 84 to moveinto driving engagement with drive sprocket clutch teeth 93 (as shown,for example, in FIG. 3).

Returning to FIG. 1, a chain 94 interconnects drive sprocket 68 with adriven sprocket 96 formed on a front output shaft 32. Front output shaft32 is supported and retained in housing 12 by suitable bearingassemblies 98 and 100. An output yoke 102 is secured to the forward endof front output shaft 32 and is adapted for connection to the frontpropeller shaft (not shown) for driving the front axle assembly and thefront set of ground-engaging wheels of the motor vehicle. As will beappreciated, a similar yoke (not shown) is secured to the rearward endof rear output shaft 30 and is adapted for connection to the rearpropeller shaft (not shown) for driving the rear axle assembly and therear set of ground-engaging wheels of the motor vehicle.

In accordance with the preferred embodiments of the present invention,integrated planetary gear assembly 28 is a "dual-planetary" arrangementhaving first and second sun gears 104 and 106, respectively, that areadapted to drive or be driven by first and second sets of planet gears108 and 110, respectively, that are supported for rotation from a commoncarrier assembly 112. Carrier assembly 112 includes a first carrier ring114, a center plate 116, and a second carrier ring 118 that are suitablyjoined such as by a plurality of bolts 120, and having formed thereoninternal splines 122, 124, and 126, respectively. First sun gear 104 hasa different diameter than second sun gear 106, both of which arelaterally spaced and axially positioned between first carrier ring 114and center plate 116, and between center plate 116 and second carrierring 118, respectively. In addition, first and second sun gears 104 and106, respectively, are further restrained against axial movement withincarrier assembly 112 by suitable thrust washers 132 and thrust bearings134.

First sun gear 104 is formed with first and second sets of laterallyspaced internal clutch teeth 136 and 138, respectively. As will bedetailed, the first set of clutch teeth 136 is adapted to be selectivelyengagable with the second set of clutch teeth 46 on rear output shaft 30in response to axial sliding movement of planetary gear assembly 28.Likewise, the second set of clutch teeth 138 are adapted for selectiveengagement with the external gear teeth of input gear 26 in response tostill further axial movement of planetary gear assembly 28. Furthermore,second sun gear 106 is formed with a single set of internal clutch teeth140 that are slidably engagable with either of the second set of clutchteeth 62 on drive sleeve 58 or clutch teeth 56 on reaction ring 54 uponaxial movement of integrated planetary gear assembly 28 along centralaxis 14. It will be appreciated that axial movement of planetary gearassembly 28 is also accomplished utilizing the shift mechanism having asecond shift member (not shown) engaged with an annular groove 142formed in first carrier ring 114. Thus, the shift mechanism is operablefor controlling axial movement of planetary gear assembly 28 and modeshift sleeve 84, such shift mechanism being manually or remotely (i.e.,motor driven, hydraulically displaced or the like) actuated.

As noted, carrier assembly 112 is adapted to rotatably support the firstset of full-length planet gears 108 and the second set of half-lengthplanet gears 110, shown in phantom in FIG. 2. Preferably, the first setof full-length planet gears 108 extend longitudinally substantially thefull axial extent between first and second carrier rings 114 and 118.Likewise, the second set of half-length planet gears 110 extendlongitudinally substantially the full axial extent between center plate116 and second carrier ring 118. Moreover, the full-length planet gears108 are journally supported for rotation on first pins 128 whilehalf-length planet gears 110 are journally supported for rotation onsecond pins 130, also shown in phantom in FIG. 2. First sun gear 104 isin meshed engagement with the first set of full-length planet gears 108while second sun gear 106 is in meshed engagement with the second set ofhalf-length planet gears 110. In addition, each one of the second set ofhalf-length planet gears 110 is intermeshed with an associated one ofthe first set of full-length planet gears 108. Thus, when transfer case10 is operating in a full-time four-wheel drive mode, integratedplanetary gear assembly 28 functions to divide the input torque suppliedto rear and front output shaft 30 and 32, respectively, in a mannerproportional to the number of teeth on first and second sun gears 104and 106, respectively.

Shifting of transfer case 10 into its various drive modes isaccomplished by axially sliding mode shift sleeve 84 and/or planetarygear assembly 28 along central axis 14, thereby selectively couplingvarious driven elements thereof with the transfer case input and outputmembers. With reference now to FIGS. 2 through 6, the various drivemodes of transfer case 10 will now be described. In the two-wheelhigh-range mode position of FIG. 2, planetary gear assembly 28 islocated at position "A" and mode shift sleeve 84 is located at adisengaged "X" position. In this arrangement, drive torque istransferred from input shaft 16 to carrier assembly 112 via engagementof the external gear teeth on input gear 26 and splines 122 on firstcarrier ring 114. Moreover, drive torque is transferred from carrierassembly 112 to rear output shaft 30 since internal splines 124 oncenter plate 114 meshingly engage the first set of clutch teeth 44 onrear output shaft 30. Thus, rear output shaft 30 is directly driven atthe same rotational speed as input shaft 16. In addition, input shaft 16is also directly coupled to drive sleeve 513 through engagement ofinternal splines 126 on second carrier ring 118 with the first set ofclutch teeth 60 on drive sleeve 58. However, since mode shift sleeve 84is maintained in its disengaged "X" position, no drive torque istransferred from drive sleeve 58, hub 72 and mode shift sleeve 84 todrive sprocket 68. Therefore, front output shaft 32 is not drivinglycoupled to input shaft 16, whereby the two-wheel high-range mode isestablished.

With reference to FIG. 3, transfer case 10 is shown shifted into itspart-time four-wheel high-range operating mode. More particularly,planetary gear assembly 28 is maintained in the "A" position such thatinput torque is directly transmitted from input shaft 16 to both rearoutput shaft 30 and drive sleeve 58 via carrier assembly 112. However,mode shift sleeve 84 is shown moved from the disengaged "X" position toan engaged "Y" position. Thus, drive sleeve 58 is now coupled to drivesprocket 68 for driving front output shaft 32. Since carrier assembly112 is directly coupled for driving both front output shaft 32 and rearoutput shaft 30 at the same speed, speed differentiation therebetween isinhibited.

In FIG. 4, planetary gear assembly 28 is shown positioned so as to placetransfer case 10 in the full-time four-wheel high-range mode withinteraxle differentiation permitted between rear output shaft 30 andfront output shaft 32. More particularly, planetary gear assembly 28 isshown moved forward along central axis 14 to the "B" position while modeshift sleeve 84 is maintained in the engaged "Y" position. As is shown,first carrier ring internal splines 122 remain in driven engagement withthe teeth of input gear 26, while the first set of clutch teeth 136 offirst sun gear 104 are intermeshed with the second set of clutch teeth46 on rear output shaft 30. Concurrently, clutch teeth 140 of second sungear 106 meshingly engage the second set of clutch teeth 62 on drivesleeve 58. In addition, internal splines 124 and 126 of center pate 116and second carrier ring 118, respectively, are disengaged from othercomponents such that carrier assembly 112 is rotatably driven about axis14. Thus, input torque is transferred via the first and second sets ofplanet gears 108 and 110, respectively, to the first and second sungears 104 and 106, respectively, for driving rear and front outputshafts 30 and 32, respectively. Since the first and second sets ofplanet gears 108 and 110, respectively, remain free to orbit about firstand second sun gears 104 and 106, respectively, differential rotationalspeeds may be accommodated between rear output shaft 32 and front outputshaft 30 without the buildup of potentially damaging excessive torqueloads. Thus, in this arrangement, a full-time high-range four-wheel modeis established with differential action permitted between front and rearoutput shafts 32 and 30, respectively.

With reference to FIG. 5, planetary gear assembly 28 is shown movedalong central axis 14 to the "C" position, while mode shift sleeve 84 ismaintained in the engaged "Y" position. As is shown, internal splines122 of first carrier ring 114 are still maintained in engagement withinput gear 26. However, center plate 116, second carrier ring 118, firstsun gear 104 and second sun gear 106 are disengaged from the outputmembers. Thus, no drive torque is transferred from carrier assembly 112to either of the front and rear output shafts, whereby transfer case 10is maintained in a "neutral" state.

FIG. 6 illustrates planetary gear assembly 28 moved to the "D" positionwith shift sleeve 84 still maintained in the engaged "Y" position. Moreparticularly, forward carrier internal splines 122 are moved out ofengagement with input gear 26 while the second set of clutch teeth 138on first sun gear 104 are moved into meshing engagement therewith. Inaddition, center plate internal splines 124 engage the second set ofclutch teeth 46 of rear output shaft 30 while internal splines 126 ofsecond carrier ring 118 engage the second set of clutch teeth 62 ondrive sleeve 58. Moreover, second sun gear 106 is grounded (i.e.prevented from rotating) by the engagement of clutch teeth 140 withclutch teeth 56 of reaction ring 54. In this arrangement, input gear 26drives first sun gear 104 at the rotational speed of input shaft 16.Thus, due to the braked engagement of second sun gear 106 with reactionring 54, rotation of first sun gear 104 causes first planet gears 108and second planet gears 110 to orbit about second sun gear 106, therebydriving carrier assembly 112 at a reduced rotational speed. As such,output shafts 30 and 32 are driven at the reduced ratio speed throughthe engagement of center plate internal splines 124 with output shaftsecond clutch teeth 46 and second carrier plate internal splines 126with drive sleeve second clutch teeth 62. Thus, a reduced ratio orpart-time four-wheel low-range drive mode is established.

With reference to FIG. 7, an alternative embodiment of an integratedplanetary gear assembly 150 is shown that is substantially similar instructure and function to integrated planetary gear assembly 28 with theexception that the entire unit is adapted to be shifted between atwo-wheel high-range mode position and a four-wheel high-range modeposition. In general, integrated planetary gear assembly 150 is operablyinstalled between input shaft 16 and first and second output members oftransfer case 10 for axial sliding movement relative thereto, suchmovement establishing the two-wheel drive mode and various four-wheeldrive modes. More particularly, integrated planetary gear assembly 150is axially movable between four distinct positions for establishing thetwo-wheel high-range mode, the part-time four-wheel high-range mode, afull-time four-wheel high-range mode, and a part-time four-wheellow-range mode. Thus, integrated planetary gear assembly 150 discloses anon-synchronized arrangement wherein drive sleeve 58 and drive sprocket68 of planetary gear assembly 28 are now integrated into a drive member152 such that mode shift sleeve 84 is not utilized for selectivelycoupling such components. For purposes of brevity, like numbersdesignate similar components to those previously disclosed while primednumbers identify those components that have been slightly modified tofacilitate the modified operational characteristics of planetary gearassembly 150.

With continued reference to FIG. 7, the various drive modes will now bedescribed. In the two-wheel high-range mode position shown, planetarygear assembly 150 is located at position "E". In this arrangement, drivetorque is transferred from input shaft 16 to carrier assembly 112' viaengagement of the external gear teeth on input gear 26 with internalsplines 122 on first carrier ring 114. Since internal splines 124' oncenter plate 114' engage clutch teeth 44 on rear output shaft 30, drivetorque is transferred from carrier assembly 112' to rear output shaft 30such that rear output shaft 30 is driven at the same rotational speed asinput shaft 16. As can be seen, drive sleeve portion 58' of drive member152 is not coupled to second sun gear 104 or second carrier ring 118',whereby no drive torque is transferred to drive sprocket 68' and, inturn, to front output shaft 32. Thus, front output shaft 32 is notcoupled to input shaft 16 for establishing the two-wheel high-range modeof operation.

Movement of planetary gear assembly 150 along axis 14 to position "F"establishes the part-time four-wheel high-range mode. In this position,input gear 26 remains coupled to first carrier ring 114' while rearoutput shaft 30 remains coupled to center plate 116' via engagement ofclutch teeth 44 and internal splines 124'. However, such movement ofplanetary gear assembly 150 cause the first set of internal splines 126on second carrier ring 118' to meshingly engage the first set of clutchteeth 60 formed on drive sleeve portion 58' of drive member 152. Thus,drive member 152 is coupled to carrier assembly 112' for transferringdrive torque to drive sprocket 68' and front output shaft 32. Moreover,since carrier assembly 112' directly couples input shaft 16 to both ofthe front and rear output shafts, they are driven at the same rotationalspeed and speed differentiation therebetween is inhibited.

Continued movement of integrated planetary gear assembly 150 to theposition identified as "G", is operable for establishing the full-timefour-wheel high-range mode wherein differential action between front andrear output shafts 32 and 30, respectively, is permitted. In thisposition, input gear 26 remains drivingly coupled to front carrier ring114 while center plate 116' and second carrier ring 118' becomedisengaged from other components such that carrier assembly 112' acts asan input member as it rotates about central axis 14. Concurrently,clutch teeth 136 of first sun gear 104 intermesh with the second set ofclutch teeth 46 on rear output shaft 30. Likewise, clutch teeth 140 onsecond sun gear 106 intermesh with the second set of clutch teeth 62 ondrive sleeve portion 58' of drive member 152. Thus, input torque istransferred from the first set of planet gears 108 to rear output shaft30 via first sun gear 104. Furthermore, input torque is transferred fromthe second set of planet gears 110 to drive member 152 and front outputshaft 32 via second sun gear 106. Since the first and second sets ofplanet gears 108 and 110, respectively, orbit about their respective sungears, differential rotational speeds can be accommodated between frontand rear output shafts 32 and 30, respectively.

Finally, upon movement of integrated planetary gear assembly 150 to the"H" position, a part-time four-wheel low-range mode of operation isestablished. In this position, internal splines 122 or first carrierring 114 are moved out of engagement with input gear 26 while clutchteeth 138 on first sun gear 104 are moved into meshing engagement withinput gear 26 In addition, center plate internal splines 124' engage thesecond set of clutch teeth 46 of rear output shaft 30 while a second setof internal splines 154 formed on second carrier ring 118' engage thefirst set of clutch teeth 60 on drive sleeve portion 58' of drive member152. Moreover, second sun gear 106 is grounded (i.e., prevented fromrotating) by the engagement of clutch teeth 140 with clutch teeth 56 ofreaction ring 54. In this arrangement, input gear 26 drives first sungear 104 at the rotational speed of input shaft 16. Thus, due to thebraked engagement of second sun gear 106 with reaction ring 54, rotationof first sun gear 104 causes first planet gears 108 and second planetgears 110 to orbit about second sun gear 106, thereby driving carrierassembly 112' at a reduced rotational speed. Since rear and front outputshafts 30 and 32, respectively, are directly coupled to carrier assembly112' they are driven at this reduced ratio speed with differentialaction therebetween being inhibited. Thus, a reduced ratio or part-timefour-wheel low-range drive mode is established.

With reference now to FIG. 8, another alternative embodiment of anintegrated planetary gear assembly 160 is shown that is substantiallysimilar in structure and function to the integrated planetary gearassembly 150 shown in FIG. 7 with the exception that the entire unit isadapted to be shifted between a two-wheel high-range mode, a two-wheelwith on-demand four-wheel high range mode, a part-time four-wheelhigh-range mode, a part-time four-wheel low-range mode and a neutralmode. In general, integrated planetary gear assembly 160 is operablyinstalled between input shaft 16 and first and second output members oftransfer case 10 for axial sliding movement relative thereto, suchmovement establishing the various drive modes of the transfer case 10 aswill be described. More particularly, integrated planetary gear assembly160 is axially moveable between five distinct positions for establishingthe two-wheel high-range mode, two-wheel with on-demand four-wheel highrange mode, part-time four-wheel high-range mode, part-time four-wheellow-range mode and neutral mode. Also provided and operably associatedwith the integrated planetary assembly 160 of transfer case 10 is atorque transfer device 162. Torque transfer device 162 may be of anytype including, but not limited to, electro-magnetic clutches, viscouscouplings or geared torque couplings. Suitable viscous coupling devicesare disclosed and described in the commonly assigned U.S. Pat. Nos.5,148,900 and 5,179,235 the disclosures of which are hereby expresslyincorporated by reference. A geared torque transfer device is disclosedand described in the commonly assigned U.S. patent application Ser. Nos.08/076,008 and 08/148,461 the disclosures of which are expresslyincorporated by reference. For purposes of brevity, like numbersdesignate similar components to those previously disclosed while doubleprimed reference numerals identify those components that have beenslightly modified to facilitate the modified operational characteristicsof planetary gear assembly 160.

In accordance with teaching a preferred embodiment, a torque transferdevice 162 is shown as a geared torque coupling type device. It shouldbe reiterated, however, that torque transfer device 162 may be of anytype coupling device operable for modifying the torque transfercharacteristics of integrated planetary assembly 160. The structure andfunction of geared torque coupling 162 is fully described in theaforementioned U.S. Patent Applications, and only a brief discussion isprovided here for purposes of understanding the function of the presentinvention. Geared torque coupling 162 includes an input sun gear 164 andan output sun gear 165 each of which mesh with a plurality of planetgears 168 journally supported within the device housing 171. Relativerotation of the input and output sun gears 164 and 165 cause a rapidrotation of the planet gears 168 and device housing 171. This rapidrotation initiates pumping of a viscous fluid by the planet gears 168and sun gears 164 and 165 in a closed circuitous path within housing171. The pumping of the viscous fluid within housing 171 resists thefree rotation of planet gears 168 and housing 171 thereby causing atorque transfer between input and output sun gears 164 and 165,respectively. Pumping of the viscous fluid is controlled and modified bya plurality of valve assemblies 172 disposed within the closedcircuitous fluid pumping path. The valve assemblies 172 are operable tomodify in response to changes in viscous fluid pressure, temperature orboth the flow of the viscous fluid within housing 171. The result is achange in the torque required to pump the viscous fluid, and therefore,a change in the torque transfer characteristics of geared torquecoupling 162. Valve assemblies 172 are further operable to inhibit fluidpumping action under various conditions causing geared torque coupling162 to become hydraulically locked resulting in direct torque transferbetween the input and output sun gears 164 and 165, respectively.

In the presently preferred embodiment, output sun gear 165 is formedwith an output stub shaft portion 174 which is journally supported onquill sleeve 48" by bearings 176. Stub shaft portion 174 is formed withexternal splines 178 which engage internal splines 180 formed on frontoutput sprocket 68" for providing driving torque to chain 94 and henceto front output shaft 32. Driving torque is delivered from the membersof integrated planetary gear assembly 160 to the first sun gear 164 viaexternal clutch teeth 186 of drive sleeve 182, which is journallysupported over tubular reaction sleeve 184, engaging internal clutchteeth 188 formed on input sun gear 164. Reaction sleeve 184 is journallysupported over quill sleeve 48" and provides driving torque from themembers of integrated planetary gear assembly 160 to second sun gear 165via external clutch teeth 190 engaging internal clutch teeth 194 ofoutput sun gear 165 through internal and external clutch formed on frontannular drive member 192, and hence providing torque transfer to frontoutput shaft 32 as described.

With reference to FIGS. 8 and 10, in the two-wheel drive high-range modeposition shown, planetary gear assembly 160 is located at position "I".In this arrangement, drive torque is transferred from input shaft 16 tocarrier assembly 112" via engagement of the external gear teeth on inputgear 26 with internal splines 122" on first carrier ring 114". Carrierassembly 112", in this arrangement, acts as an input member as it isthereby caused to rotate about central axis 14. Concomitantly, clutchteeth 124" of carrier ring member 116" intermesh with external clutchteeth 166b of rear annular drive member 168b, the internal clutch teeth170b of which engage external splines 172 of rear output shaft 30".Thus, input torque is transferred from input shaft 16 to rear outputshaft 30" for providing a two-wheel drive high range mode.

With reference to FIG. 12, planetary gear assembly is shown shifted toposition "J" for establishing the two-wheel with on-demand four wheelhigh-range mode. In this arrangement, input torque is transferred frominput shaft 16 to carrier assembly 112" via engagement, of the externalgear teeth on input gear 26 with internal splines 122" on first ringmember 114", and carrier assembly 112" again acts as an input member.Input drive torque is transferred via carrier center ring 116" to rearoutput shaft 30" via engagement of clutch teeth 124" with externalclutch teeth 166b of rear annular drive member 168b, the internal clutchteeth 170b of which engage external splines 172 of rear output shaft30". Concomitantly, clutch teeth 126" engage clutch teeth 198 of drivesleeve 184 for providing driving torque to input sun 164 of torquecoupling 162. Under normal driving conditions, i.e., when traction isbeing generated at the rear ground engaging wheels, input sun gear 164is driven at the same rotational velocity as rear output shaft 30".Output sun gear 165, under normal driving conditions, is rotated atsubstantially the same rotational velocity as input sun gear 164 due tothe rotation of the front ground engaging wheels coupled to front outputshaft 32, chain 94 and sprocket 68". However, under driving conditionswhere the rear ground engaging wheels experience a loss of traction,such as on wet or ice covered road surfaces, torque is automaticallytransferred to the front ground engaging wheels for initiating theon-demand four-wheel drive mode.

As previously mentioned, and as described more fully in patentapplication Ser. Nos. 08/076,008 and 08/148,461, when there is norelative rotation between input and output sun gears 164 and 165, torquecoupling 162 does not act to transfer torque. Thus, in the presentarrangement and under normal operating conditions both the input andoutput sun gears 164 and 165 rotate at substantially the same rotationalvelocity, as described, and no torque is transferred to the front groundengaging wheels. In the preferred embodiment, a slight relative rotationis maintained between the input and output sun gears for continuouslyoperating torque coupling 162 at a low level under normal operatingconditions. When traction is reduced or lost at the rear ground engagingwheels, there is a tendency to drive these wheels at a higher rotationalvelocity, i.e., a rotational velocity exceeding the rotational velocityassociated with a given motor vehicle speed and, for example, spinningthe rear wheels. The front ground engaging wheels rotational velocityremains substantially unchanged. As will be appreciated, the result is arotational velocity differential between the front and rear groundengaging wheels, and hence, between output sun gear 165 and the inputsun gear 164. Torque coupling 162 resists the tendency toward arotational velocity difference, however, by the internal fluid pumpingaction describe. The response of torque coupling 162, therefore, is totransfer torque from the input sun gear 164 to the output sun gear 165and hence to the front ground engaging wheels for establishing theon-demand four wheel drive mode. As will be appreciated, when drivingconditions return to normal, i.e., traction is restored to the rearground engaging wheels, the difference in rotational velocity betweenthe input and output sun gears is eliminated and a two-wheel drive modeof operation is restored. It should also be understood that transfercase 10 may be arranged such that the front ground engaging wheels aredriven in the two-wheel drive mode and torque transferred to the rearground engaging wheels on-demand upon a loss of traction at the frontground engaging wheels.

With reference to FIG. 13, with planetary gear assembly 160 shifted tothe position marked "K" a part-time four-wheel drive high-range mode isestablished. In this mode, input gear 26 clutch teeth engage carrierfirst ring 114" clutch teeth 122", and carrier 112" acts as an inputmember driven at input shaft 16 rotational velocity. Rear output shaft30" is coupled to carrier center plate 116" via engagement of clutchteeth 124" with rear annular drive member 168b clutch teeth 166b, andrear output annular drive member 168b internal clutch teeth 170bengaging rear output shaft 30" clutch teeth 172. Rear ring member 118"clutch teeth 126" engage reaction sleeve 184 clutch teeth 196b forproviding driving torque via output sun gear 165 to front output shaft32. Second sun gear 106" clutch teeth 140" engage reaction sleeve 184clutch teeth 196a, however, this engagement is of no consequence asfirst sun gear 104" clutch teeth 136" are not engaged with an outputmember. As will be appreciated, both the rear and front output shafts 30and 32, respectively, are driven at the input shaft rotational velocitywith differentiation therebetween inhibited thus establishing apart-time four-wheel drive high range mode.

With reference to FIG. 9, integrated planetary assembly is shown shiftedto the neutral position indicated at "L". As can be seen, input shaftgear teeth 26 engage first sun gear 104" clutch teeth 136", and secondsun 106" clutch teeth 140" engage reaction sleeve clutch teeth 196a.Carrier first plate 114" clutch teeth 122", carrier center plate 116"clutch teeth 124" and second ring 118" clutch teeth 126" do not engageinput or output elements, and planetary gear assembly 160 is allowed torotate freely for establishing the neutral mode.

With reference to FIG. 11, upon movement of integrated planetary gearassembly 160 to the "M" position, a part-time four-wheel low-range modeof operation is established. In this position, internal splines 122" onfirst carrier ring 114" are moved out of engagement with input gear 26while clutch teeth 136" on first sun gear 104" are moved into meshingengagement with input gear 26. In addition, center plate internalsplines 124" engage rear annular drive member clutch teeth 166a forproviding output to rear output shaft 30" while internal splines 126"formed on second carrier ring 118" engage external clutch teeth 196a ofdrive sleeve reaction sleeve 184. Second sun gear 106" is grounded(i.e., prevented from rotating) by the engagement of clutch teeth 140"with clutch teeth 56 of reaction ring 54. In this arrangement, inputgear 26 drives first sun gear 104" at the rotational speed of inputshaft 16. Thus, due to the braked engagement of second sun gear 106"with reaction ring 54, rotation of first sun gear 104" causes firstplanet gears 108 and second planet gears 110 to orbit about second sungear 106", thereby driving carrier assembly 112" at a reduced rotationalspeed. Since rear output shaft 30" is directly coupled to carrierassembly 112" and front output shaft 32 is coupled to carrier 112" viareaction sleeve 184 and second sun gear 165, they are driven at thisreduced ratio speed with differential action therebetween beinginhibited. Thus, as can be appreciated, a reduced ratio or part-timefour-wheel low-range drive mode is established.

While specific embodiments have been shown and described in detail toillustrate the principles of the present invention, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles. For example, one skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as described in the following claims.

What is claimed is:
 1. A transfer case for a four-wheel drive vehiclecomprising:a housing; an input member supported for rotation in thehousing; first and second output means supported for rotation in thehousing; a planetary gear assembly that is axially moveable relative tothe input member and the first and second output means between aplurality of positions for establishing a plurality of drive modes atleast one of which is a two-wheel drive high-range with on-demandfour-wheel drive high-range mode; and torque coupling means disposedbetween the planetary gear assembly and the second output means forselectively transferring torque to the second output means in responseto the traction experienced by the first output means and when theplanetary gear assembly is in the two-wheel high-range with on-demandfour-wheel high-range mode position for establishing the on-demandfour-wheel high-range mode.
 2. The transfer case of claim 1 wherein thetorque coupling means is further operable for directly coupling thefirst and second output means.
 3. The transfer case of claim 2 whereinthe torque coupling means includes a geared torque coupling.
 4. Thetransfer case of claim 2 wherein the torque coupling means includes aviscous coupling.
 5. A transfer case for a four-wheel drive vehiclecomprising:a housing; an input member supported for rotation in thehousing; first and second output means supported for rotation in thehousing; a planetary gear assembly having a first sun gear, a pluralityof first planet gears meshed with the first sun gear and journalled on acarrier, a second sun gear, and a plurality of second planet gearsmeshed with the second sun gear and journalled on the carrier with eachof the second planet gears being meshed with an associated one of thefirst planet gears, the planetary gear assembly being axially moveablerelative to the input member and the first and second output meansbetween a first position for establishing a two-wheel high-range mode, asecond position for establishing a two-wheel high-range with on-demandfour-wheel high-range mode, a third position for establishing apart-time four-wheel high-range mode, a fourth position for establishinga part-time four-wheel low-range mode and a fifth position forestablishing a neutral mode; and torque coupling means disposed betweenthe planetary gear assembly and the second output means for selectivelytransferring torque to the second output means in response to tractionexperienced by the first output means and when the planetary gearassembly is in the two-wheel high-range with on-demand four-wheelhigh-range mode position for establishing the on-demand four-wheel drivehigh-range mode.
 6. The transfer case of claim 5 wherein the firstoutput means is operably coupled to a first set of ground-engagingwheels and the second output means is operably coupled to a second setof ground-engaging wheels.
 7. The transfer case of claim 6 wherein thetorque coupling means is further operable for directly coupling thefirst and second output means.
 8. The transfer case of claim 7 whereinthe torque coupling means includes a geared torque coupling.
 9. Thetransfer case of claim 7 wherein the torque coupling means includes aviscous coupling.
 10. The transfer case of claim 6 wherein when theplanetary gear assembly is shifted to the first position, the inputmember is coupled to the carrier, the carrier is coupled to the firstoutput means and the second output means is uncoupled from the inputmember.
 11. The transfer case of claim 6 wherein when the planetary gearassembly is shifted to the second position, the input member is coupledto the carrier and the torque coupling means, the carrier is coupled tothe first output means and the torque coupling means is coupled to thesecond output means.
 12. The transfer case of claim 6 wherein when theplanetary gear assembly is shifted to the third position, the inputmember is coupled to the carrier and the carrier is coupled to the firstand second output means.
 13. The transfer case of claim 6 wherein whenthe planetary gear assembly is shifted to a fourth position, the inputmember is coupled to the first sun gear, the carrier is uncoupled fromthe first and second output means, and the second sun is coupled to thetorque coupling means.
 14. The transfer case of claim 6 wherein when theplanetary gear assembly is shifted to the fifth position, the inputmember is coupled to the first sun gear, the second sun gear is coupledto the housing and the carrier is directly coupled to the first andsecond output means.
 15. A full-time four wheel drive transfer casecomprising:a housing; an input shaft adapted to be driven by an outputshaft of a vehicle drivetrain; a first output shaft adapted to becoupled to a first set of ground-engaging wheels of a vehicle; a secondoutput shaft and drive means adapted to be coupled between the planetarygear assembly and the second output shaft for delivering drive torquefrom the input shaft to the second output shaft, the second output shaftbeing adapted for interconnection to a second set of ground-engagingwheels of a vehicle; a planetary gear assembly that is axially moveablerelative to the input shaft and the first and second output shafts andhaving a first sun gear, a plurality of first planet gears meshed withthe first sun gear and journalled on a carrier, a second sun gear, and aplurality of second planet gears meshed with the second sun gear andjournalled on the carrier with each of the second planet gears beingmeshed with an associated one of the first planet gears; torque couplingmeans disposed between the planetary gear assembly and the second outputmeans for selectively transferring torque to the second output shaft inresponse to loss of traction experienced by the first output shaft andwhen the planetary gear assembly is the two-wheel drive high-range withon-demand four-wheel drive high-range mode position thereby establishingthe on-demand four-wheel drive high-range mode; the planetary gearassembly being moveable between: a first position for establishing atwo-wheel high-range mode where the input member is coupled to thecarrier, the carrier is coupled to the first output means and the secondoutput means is uncoupled from the input member; a second position forestablishing a two-wheel with on-demand four-wheel high-range mode wherethe input member is coupled to the carrier and the torque couplingmeans, the carrier is coupled to the first output means and the torquetransfer device is coupled to the second output means; a third positionfor establishing a part-time four-wheel high-range mode where the inputmember is coupled to the carrier and the carrier is coupled to the firstand second output means; a fourth position for establishing a neutralmode where the input member is coupled to the first sun gear, thecarrier is uncoupled from the first and second output means, and thesecond sun is coupled to the torque transfer means; and a fifth positionfor establishing a part-time four-wheel low-range mode where the inputmember is coupled to the first sun gear, the second sun gear is coupledto the housing and the carrier is directly coupled to the first andsecond output means.
 16. The transfer case of claim 15 wherein thetorque coupling means is further operable for directly coupling thefirst and second output shafts.
 17. The transfer case of claim 15wherein the input member is an input shaft driven by an output shaft ofa drivetrain for the vehicle, the first output means is a first outputshaft adapted to be coupled to a first set of ground-engaging wheels ofthe vehicle, and the second output means includes a second output shaftand drive means adapted to be selectively coupled between the planetarygear assembly and the second output shaft for delivering drive torquefrom the input shaft to the second output shaft, the second output shaftbeing adapted for interconnection to a second set of ground-engagingwheels of the vehicle.
 18. The transfer case of claim 16 wherein thetorque coupling means comprises a geared torque coupling.
 19. Thetransfer case of claim 16 wherein the torque coupling means comprises aviscous coupling.
 20. The transfer case of claim 16 wherein the torquecoupling means is further operable for decoupling the first and secondoutput means in response to a restoration of traction to the firstoutput shaft.